The condensation reactions of aldehydes, and particularly the condensation reactions of phenols and aldehydes are, or can be, quite violent, inasmuch as they generate a considerable amount of heat. Aldehyde condensate resins are relatively cheap and have been used as binders for molded articles, and foundry molds, for a long time. Aldehydes can be reacted with donors of hydrogen atoms, as for example, benzene rings containing hydroxyl groups, amines including urea, dicyandiamide, and melamine, etc., to form alkanol groups which then react with other hydrogen donors by splitting off water. These reactions liberate a considerable amount of heat and because water is also liberated, the aldehyde condensate resins are usually made in water solutions. Some control of the reaction is usually achieved by flashing water from the solutions. In addition the reactions are usually carried out in kettles containing cooling coils or jackets, so that the reactions can be stopped before the condensate resins reach a completely crosslinked and infusible state. The fusible partial condensates at this point are usually solids at room temperature and are used as binder forming materials for porous articles and electrical applicators.
The fusible B staged aldehyde condensates give off water when they react with further aldehyde to produce the infusible C-stage. When such aldehyde condensates are to be used as molding compounds, they are mixed with fillers, and are compressed between heated surfaces to cross-link the partial condensates. One of the problems with such molding compounds is that the water liberated tends to decrease the bond strength that is produced with the fillers and/or it produces porosity in the finished molded article.
Where the partial condensates are to be used to produce porous structures, such as insulation, foundry molds, etc. water escapes during molding without deliterous effects. Heretofore, aldehyde condensates, and particularly phenol formaldehyde have been limited to such useage.
Resorcinol and aldehyde have also been added to aqueous mixtures of portland cement and sand (concrete) to produce a high early strength without changing the crystal structure of the hydraulic cement (see Column 4, Collins et al. U.S. Pat. No. 3,216,966). No particular problem is produced by the heat and water liberated in concrete because the reactants comprise such a small percentage of the materials present.
In a recent U.S. Pat. No. 3,944,515 there is disclosed a process wherein the reaction of portland cement, phenol, formaldehyde, and urea is carried out in the presence of ice in a stainless steel vessel that is equipped with an agitator and an indirect heat exchanger. Even though ice is utilized, the reaction gives off so much heat that the control of the reaction requires constant attention and special equipment for removing the heat of the reaction.
An object of the present invention is the provision of a new and improved method of producing a molding compound whose binder is an aldehyde condensate resin that is so controllable that the molding compound can be made from monomers without first making a precondensate.
A further object of the present invention is the provision of a new and more controllable process for reacting phenols and aldehydes.
Further objects and advantages of the invention will become apparent from the following description of the preferred embodiments.
In order that the advantages of the present invention will be more readily apparent, an understanding of the prior art as above described should first be understood.
As used in the present specification, the term aldehydes will be used to connote materials represented by the general formula RCHO as well as polymers thereof, and will include formaldehydes, acetylaldehyde, paraformaldehyde, etc. The term phenol materials is used in the broad sense to connote all materials containing a phenolic hydroxyl group, i.e. an OH group on a benzene ring, as for example, phenol - the lower member of the group, rescorcinol, catacol, etc. which are mildly acidic in nature and have three or more labile hydrogens.